1. Field of the Invention
This invention relates to packing material and packing preferably suitable to gland packing or the like for use in a shaft seal part of a hydraulic machine.
2. Prior Art
A variety of gland packings in which flexible graphite is used as a base material have been hitherto known for use in a shaft seal part or the like portion of a hydraulic machine, for example.
Gland packings of this sort are manufactured by various techniques, such as laminating, die molding, chip molding, and ribbon packing. However, these techniques require that the graphite material must be previously molded into a ring shape conforming to the diametral size of a shaft with which such packing is to be used; as such, the packing cannot be used with any shaft having a different diameter. Therefore, such packing lacks versatility in use. Another, difficulty with such packing is that since flexible graphite is of low tensile strength and brittle in itself, once the packing is mounted in position it is extremely difficult to remove same when replacement is required, which means less usability.
Further, the aforesaid manufacturing techniques individually have drawbacks of their own. The laminating technique involves the problem of poor yield, which leads to higher cost. Where the die molding or chip molding technique is employed, dies or metal molds are required, which means higher cost, and the packing produced is less versatile. The ribbon packing technique does not provide good workability. These difficulties may be overcome by forming the flexible graphite into a cord-like structure so that it may be used by being cut to a specified length conforming to the diameter of the shaft, as is the case with such other type of packing as fiber braided or knitted; but the trouble is that flexible graphite cannot be braided or knitted because, as pointed out above, it is in itself of low tensile strength and so brittle that its compressibility and allowable limit of twist are both extremely low. Therefore, it has hitherto been considered impossible to use such packing in such a way as is usual with the aforesaid fiber braided or knitted type of packing, that is, in such a way that the braided or knitted packing is cut to a length according to the diametral size of the shaft with which it is to be used, the so cut packing being then wound about the outer periphery of the shaft.